Robot Teach... Safety Requirements?

Brian Hamilton · Apr 17, 2008

I have a project with a large array of servo drives, as part of the setting up sequence i want to follow the way robot's work during teach mode - ideally during setup reducing all the drives into a "reduced power/speed" mode and allow access into the hazard zone without tripping the lazer scanner protecting the area.

My main thought however is how do you safely set a drive to "reduced power/speed" etc, i can set a definative input on the CNC controller to overide any commands from the program but can it be classed as safe if you are relying on the CNC controller?

How do robot manufactures get around verifiying its safety??

I would be keen to know if any one has had any similar issues in the past or has any suggestions??

CharlesM · Apr 17, 2008

What hardware will you be using?

hokie · Apr 17, 2008

You need a servo drive with category 3 safety, that supports safe motion.
They have a redunant saftey board that monitors the motion along with drive. A few manufacturers make that type of product. See below link:

http://www.boschrexroth.com/busines...indradrive_en/sicherheitstechnik_en/index.jsp

craig_avanzar · Apr 18, 2008

How do robot manufactures get around verifiying its safety??

I'm not sure how this applies but the robots I am around have a deadman switch on the pendant. The pendant must be in hand and the switch is moved to the halfway point of its action in order for the servos to come in. Any operation other than that requires all safeties to be functioning properly like safety gates closed, light curtains clear, pressure mats clear, etc.

Brian Hamilton · Apr 18, 2008

Thanks for the replys...

I did consider going down the "deadman's handle" but after speaking to the operators/customer some of the operations such as tooling changes require two hands free.

We are planning on using Baldor moti-flex drives with a nextmove e100 controller all linked together with ethernet.

Any other suggestions welcome?

jstolaruk · Apr 18, 2008

hokie said:
You need a servo drive with category 3 safety, that supports safe motion.
They have a redunant saftey board that monitors the motion along with drive. A few manufacturers make that type of product. See below link:

http://www.boschrexroth.com/busines...indradrive_en/sicherheitstechnik_en/index.jsp

This explains it perfectly. The Fanuc robots I'm programming now will not allow the servos to run over 250mm/sec when the teach pendant is enabled and the deadman switch on the back of the pendant comes into play with the E-stop circuit. There is also a optional deadman switch to allow a 2nd person in the cell.

LadderLogic · Apr 18, 2008

Brian Hamilton said:
Any other suggestions welcome?

I guess the only other way is to design the mechanical part of the system in such a way that nothing moves on its own when the servos are disabled. Which could mean, depending on situation, motors with brakes, disengaging air springs etc.

I am yet to see a servo manufacturer that would offer a drive with "safe lock" function - some kind of safety-rated circuit that would keep servo enabled at zero speed rather that disable it. Then, a combination of a keyswitch, gurads bypass relay and a deadman switch might be used for slow jogging.

panic mode · Apr 18, 2008

I would have to agree with ladderlogic,

i have not seen one system that would have control reliable speed limit function in the drive. one can use safety circuit to send signal to drive to enable speed limiting (via external speed reference or drive parameter) but this is still not safety rated input/function.

teaching is manual function (so be alert and hold on that enabling device aka dead man switch). standard these days is 3-pos switch which enables drives if the switch is in mid position (squeezing or releasing causes safe stop).

if anyone is aware of motion system that works differently (has control reliable speed limit functuion), i would like to know about it.

hokie · Apr 18, 2008

LadderLogic said:
I am yet to see a servo manufacturer that would offer a drive with "safe lock" function - some kind of safety-rated circuit that would keep servo enabled at zero speed rather that disable it. Then, a combination of a keyswitch, gurads bypass relay and a deadman switch might be used for slow jogging.

I have done this before...
You can buy drives that allow EN954-1 category 3 safe motion from many manuafactures: Bosch Rexroth, B&R, Siemens, Lenze ...
They cover things like safe limit velocity, safe motion limits, incremental distances, etc. This is been availible for several years.
This is seen on many CNC machines for setup, printing machines for threading, Robot cells for teaching points with operators in the work cell, etc.

panic mode · Apr 19, 2008

do you have sample part number? i'd like to check that out.
there is number of drives out there that have "safety integrated" etc meeting Cat3 but this was always only for drive enable, nothing else...

Bratt · Apr 19, 2008

Siemens Sinamics S120 has safe speed

panic mode · Apr 19, 2008

thank you. i've read the link and checked documentation (have bunch of big manuals) but
still can't find how to limit speed - on demand - and safely...
any pointers?

Bratt · Apr 20, 2008

Here is a manual on how to do it with G120 their regular VFD drive. I belive its the same principle with the Servo's. You set up safe parameters with the configuration software for the servo and then you send commands over profisafe (Profibus or Profinet) to go down to safe speed and then the drive does all the monitoring and shuts down in case of fault. I'm actually going to use a S120 with safe speed in an aplication so in a couple of weeks i will know exactly if you need any examples.

Robot Teach... Safety Requirements?

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